The use of belt transport systems is known including those systems useful in moving media through various marking stations in a xerographic apparatus. In these apparatuses, paper sheets or media are fed to a moving system transport belt. Generally, vacuum belt transport systems used in the prior art will only provide a consistent vacuum force over the length of the transport belt. These prior art transport systems do not provide different levels of variable vacuum. Although these vacuum belt systems consisting of a vacuum suction and a vacuum belt with holes aligned with vacuum plenums may be adequate for providing a consistent vacuum force over the length of a transport, when differing levels of vacuum are needed this arrangement does not provide variable vacuum.
When attempting to acquire media sheets from an upstream transport belt or stack, a higher acquisition vacuum force is often needed to acquire the media to the vacuum belt than is needed to transport the media once it is acquired. Any additional vacuum from acquisition that is translated to the transport portion through continuous plenums running through the transport portion lowers the overall pressure for acquisition due to losses around the media. A typical prior art vacuum transport system is described in U.S. Pat. Nos. 7,293,770 and 5,967,510.
In systems where it is necessary for a vacuum belt transport to both acquire the media and also to transport the media, the additional vacuum needed during acquisition must be balanced with the lower vacuum requirements needed during transport.
Vacuum belt transports make use of aligning belt holes with an underlying vacuum plenum. When the media is covering the holes, the media is pulled against the belt and this force allows the media to be transported along with the belt translation. The more holes in contact with the media the more force can be distributed across the media. However, in the inter-media gap, the holes that are aligned with a plenum will reduce the overall vacuum pressure due to the air volume losses.